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  • More newbie equipment questions...

    Please pardon, again, what are so obviously elementary machining questions. I am still researching what I need to begin with for what I want to do...

    I'm sure this is supposed to be self explanatory, but what does the max drilling capacity for cast-iron and steel indicate? (i.e. - one grizzly mill, in particular, has a max drilling capacity for steel of 3/4" inch)

    I am actually looking at the Sherline 8-direction mill to begin with...

    If you go to www.poweredgehawaii.com/images/slidecrosssect.gif I have a very rudimentary diagram that represents a cross-section of an object that is appx 7" long. I have purposfully left out actual dimensions as I am looking for general hints regarding technique. However, the diagram is pretty close to 1:1 scale. (That may very depending on your monitor and pixel resolution, but you get the point).

    A. Outside round. - Do I need a rotary table to cut something like this? (i.e. - partial circle)

    B. Rounded corners? What's the general technique for taking a block and rounding corners like this? Does the technique differ for outside corners and inside corners?

    C. Inside bore. I'm wondering how you would bore a hole of this size all the way through the length of the 7" block? Would I need a really long tool/bit?

    Thanks much for your suggestions =)

    lance




    [This message has been edited by Cliffy15 (edited 12-30-2002).]

  • #2
    Hey guy,

    It all depends on your tolerances.

    The outside profile is relatively easy.
    Square it up. mill your shoulders and use weldon type corner rounding mills for the radaii.

    I don't know of a mill-drill that will go thru 7" in one shot.

    You are going to drill and ream both, deep as you can,lower the head re-align it and finish going thru with each tool.


    Now that slot,
    If you have a wirecut edm, it'll be done in a flash.
    But with the edm, why mill it at all, except for a starter hole.

    My best guess is a redesign.

    But you can weld a band saw blade in the large hole, and saw out the slot and finish broach, or file it.

    If it's aluminum, or plastic, you may be able to drill out some material and mill it with a .25 mill, 3.5 long from both sides.

    Or set a bar up between centers on your lathe with a parting type tool in the center, spindle locked, mount the part on the crosslide and "shape" it out by moving the carriage..

    Any other ideas, bright or otherwise?

    kapullen

    Comment


    • #3
      Lance
      A 3/4" capacity means that it can safely drill a 3/4" hole in steel with a twist drill. The Sherline is not going to be able to match that power or ridgidity.

      A. Yes

      B. Generally speaking when we machine a block we would break the corner with a chamfer. Woodworkers usually round over the corners. Round over bits are easier to get for metal working now from a few thou radius on up.

      Inside corners cut with sharp tools usually leave a sharp right angle - this can produce stress risers and as a result endmills can be purchased with radiused lips for low stress requirements.

      C. Don't know diameter, but yes it has to be drilled with a bit longer than the hole. If a precision bore is required a boring head or reamer would be used to finish it. If reamed a Spiral Flute Reamer would be required because of the interferring slot cut in the hole.

      A part 7" deep is likely unmachinable on a Sherline as the slot it has would require end mills longer than 7" and the "Z" height on the mill would have to be the length of the tool plus the clearance height over the work. This is an expensive part to make...

      Comment


      • #4
        As Kap says...it all depends on your tolerances.

        Drilling a 7" deep hole is difficult in the best of circumstances, and doing it on a Sherline is likely to be Really Difficult. One thing you might consider is (depending on your tolerances, and what it's made of) doing it as an assembly. Mill the hole C as a longitudinal groove in two halves with a ball end mill, then silver solder or otherwise put the two halves together to make a round hole...assuming it's a material you can sliver solder, or glue, or somehow stick together satisfactorily. Pull the same kind of stunt with the A part, although that gets a little more complicated because you need to mill the slot, then do the smaller hole.
        Actually, thinking about it, I guess you could slice it horizontally (as drawn) and mill halves of both holes and half the slot at the same time. Then assemble. Then you'd have only two pieces to contend with.

        As far as rounding over, the small radii B would probably most easily be done with a corner rounding end mill. The large radius A would be problematic even with a rotary table, if the piece is 7" long. If the radius falls within the range of a corner radius end mill, you could do it in two passes, one on each side, although the result wouldn't be exactly a half-circle, most likely.

        One other way to do radius A, once you get the smaller hole through, is to hold the piece on a rod, supported at the ends, so the whole piece can pivot on the rod. Then make a series of lengthwise passes with a milling cutter, turning the piece on the rod a bit each time, to create a series of flats that approximate the radius. Then finish with a file to smooth out the ridges.

        [This message has been edited by SGW (edited 12-31-2002).]
        ----------
        Try to make a living, not a killing. -- Utah Phillips
        Don't believe everything you know. -- Bumper sticker
        Everybody is ignorant, only on different subjects. -- Will Rogers
        There are lots of people who mistake their imagination for their memory. - Josh Billings
        Law of Logical Argument - Anything is possible if you don't know what you are talking about.
        Don't own anything you have to feed or paint. - Hood River Blackie

        Comment


        • #5
          Lance,

          While I have machined for the better part of the last eight years... I will tell you that I am far from being a seasoned machinist.

          What it is I would like for you to know is that you need not apologize for your questions (I hope that I CAN speak on the behalf of the group here). The neat thing about machining (you will learn this as you go along) is that there are many ways to accomplish any one facet of a project. This means that many people will have a different idea to offer to you. The other thing is machining is truely a skilled art (one that I feel does not get enough recognition). By the way, Jay Leno is a great public advocate for us! He offers praise to machinist every so often in Popular Mechanics. Anyway, you could spend your life machining (manually) and never know it all! A lesson to take to heart... don't ever get a job in a shop with a chip on your shoulder... there is surely someone around that may show you up and humble you!

          At least here we have a friendly sharing atmosphere!

          Another way to look at this... is remember no one is born with machining skill... WE ALL STARTED AT THE BEGINING LIKE YOU ARE DOING now! You should be commended for your efforts to learn!

          In knowing this you will see that there is no need for apologies and there will come a time that you too will help some "newbie" in our world of metal working.

          It will come along... don't worry.

          Also a student in machining,
          Ebob


          [This message has been edited by Eutecticbob (edited 12-31-2002).]

          Comment


          • #6
            Thanks for all of your great answers to my questions! I'm finally beginning to understand some of the vocabulary that you are all using and it now seems a little less intimidating!

            I think I have oversimplified my prospective part and I should clarify a few things:

            1. The part is, in fact, a cross section of a pistol slide. Outside round at "A" is part of the slide that contact the pistol lower frame. The radius on the inside of "A" is designed to hold a recoile guide rod and spring to return the slide to position after firing. The radius, "C", actually holds/guides the pistol barrel. However, I have over simplified as the outside round, "A", only exists in the first three inches of the part and the radius "C" exists in the first 1/4". The rest of the, for lack of appropriate terminology, "rectangle" needs to be milled out to fit replica pistol internals (essentially a large cavity).

            2. This part needs to be milled ... an assembly will not work in this particular case due to the stresses of firing (although not nearly as strong as firing a real firearm).

            3. The part will be milled from 6061 aluminum.


            While I'm at it ... one more question before I restrict myself to a bit of reading, only THEN will I ask more questions =):

            Thrud stated 'A 3/4" capacity means that it can safely drill a 3/4" hole in steel with a twist drill. The Sherline is not going to be able to match that power or ridgidity.' - I am still not well versed enough in machining to understand what this means even though Thrud has taken care to put this in easy language for me. I do not understand the reference to a twist drill. Is this somewhat akin to a horsepower unit of measurement in an automobile?

            Thanks again for all your help, support, and encouragement!

            Lance

            Comment


            • #7
              Cliffy,
              Hey, everyone has to learn to start with. The only dumb questions are ones you don't ask. I think it's great you are so willing to listen and learn.
              Twist drill is one term for drill bit.
              Good luck with all the learning. All of us can learn all the time.

              Comment


              • #8
                Lance
                Depending on the hardness of the steel drilling 3/4" hole with a twist drill would require about 1.5 HP max. To drill this hole also requires a fair amount of downward force (around 2,000lbs.) to keep the cutting edge of the drill cutting properly. This is not insignificant. A 2" hole could easily be drilled with a "core drill or annular cutter" with the same power and force.

                As to fabricating a 6061 facsimile to a .45 slide - yes you could do it on the sherline. However, the hole would not be drilled as deeply as you think - it it is easier to hollow out the slide with endmills (the real thing is done on a horizontal mill) and woodruff cutters to cut the mating groove to the frame. If you have done any wood working were a trim piece is made by sucessive use of cutters it is easy to understand the basic operation that must be performed. Use what ever method you have at hand to remove the metal you do not need - but remember, if you cut off too much you have created what we like to call "scrap", "paperweights", snafu, take your pick.

                Use what ever tools you have to remove whatever does not look like what you want!
                (the smart-ass existentialist reply)

                Comment


                • #9
                  Not "scrap" -- "learning experiences"! (I've got a box full of 'em!)
                  ----------
                  Try to make a living, not a killing. -- Utah Phillips
                  Don't believe everything you know. -- Bumper sticker
                  Everybody is ignorant, only on different subjects. -- Will Rogers
                  There are lots of people who mistake their imagination for their memory. - Josh Billings
                  Law of Logical Argument - Anything is possible if you don't know what you are talking about.
                  Don't own anything you have to feed or paint. - Hood River Blackie

                  Comment


                  • #10
                    Thrud: Now you say " Use what ever method you have at hand to remove the metal you do not need - but remember, if you cut off too much you have created what we like to call "scrap", "paperweights", snafu, take your pick."

                    Thrud IDN'T YOU tell me to just put the lathe in reverese to put metal back on? Why won't this work in a mill too? I am losing trust fast as I get more experience!

                    And see Cliff, how much I have learned from your "Dumb" question? Keep 'em comming Cliff cause I am too dumbe to think of the questions my self.
                    Steve

                    PS: you statement about vocabulary is astute. Thats the trick to learning most things- learn the language then the rest becomes either common sense are apparent. And its up to the the beginner to learn the language and to learn that the words often mean differnet things in different places, and MOST important

                    Steve

                    Comment


                    • #11
                      Steve
                      Putting material back on is easy once you accelerate the lathe spindle past lightspeed (thus reversing time) or for a 1" diameter work this would work out to about 225,573,935,091 rpm - so I would recommend a VFD...definately.

                      Maybe safety glasses too...

                      Comment


                      • #12
                        I just have to jump in on this one...

                        Thrud, actually if we went to the speed of light we would gain mass to infinity... hence... we could, in theory, all take a few chips of whatever parent metal we have and make more... BUT YOU CAN GO FIRST because I do know what the ANSI rating for safety glasses is for things moving at that velocity.

                        Ebob

                        Comment


                        • #13
                          Cliff: now you see how "dumb" questions can lead to great invinetions. My point is proved.
                          Please note that altho Thrud calculated the needed RPM, and Ebob is going to use that mass, you can not trust their figures because, among other things, the earths rotational speed was neglected in Thruds last few digits, Ebob is basing his chip mass (infinity) on Thurds erronous speeds. Thrud may add or delete rpm (partialy depending on the earth's latitide involved, but the mass is NOT infinity cause it approaches infinity as you approach light speed and becomes less when light speeds is exceeded.

                          Comment


                          • #14
                            Just a reminder, don't try that with a screw-on chuck.

                            Comment


                            • #15
                              Heh, and now my co-workers are looking at me funny now that I'm laughing at my computer screen (when, normally, I'm swearing at it).

                              Sorry to break up all of the theoretical discussions, but now that I know what the drilling capacity for a mill stands for, how does that effect the milling operations that I plan to do?

                              Does that mean that if I wanted to drill a 7" hole in steel, with my 3/4" capacity mill, I'd get 3/4" in and then POOF(!) the antimatter generated would threaten the universes' existence (notice the plurality)

                              Does the tool cutting area,diameter, speed, feed rate change any of this?

                              Or does that mean that I need to get a mill with a 3.5 horsepower motor (assuming only one axis and a linear interpolation)?

                              ... and while I have your attention, how about a few more questions?

                              I've seen many measuring templates to measure very small radii. How would I measure larger sized radii (inside & outside) over 2"? Would I need to start breaking out the scientific calculator or is there a mechanical solution to this?

                              Am I correct in assuming that milling on a machine without power feed takes a practiced hand to get a decent finish? is considerable force required to do it?

                              When machining a cavity, or "indentation" for lack of the correct term, how does one get sharp corners (i.e. - machining a semicircle or a square, or the inside corner of a "box") when one is using what is basically a rotary tool?

                              What does the term single-phase motor mean? What would I need a multi-phase motor for?

                              Has anyone figured a way to take a standard mill and use a template (like a big, metal stencil) to mill those curves in one plane (without CNC controls or power feed? (i.e. - say, just the X/Y plane)

                              Thanks in advance!

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